In the field of illumination, there is more and more expectation on solid state lighting applications, in particular, on white illumination using semiconductor light emitting diode, leading to a widespread, vigorous, and continuous research and development. Although white light emitting diode lamp has already achieved an emission efficiency greater than or equivalent to an incandescent light bulb, there is room for further improvement, and it is considered that the white light emitting diode lamp will become widespread in the near future as an energy saving illumination device. In addition, white light emitting diode lamp is substantially advantageous in that the white light emitting diode lamp does not include substances such as mercury which impose a heavy burden on the environment. Because the dimension of an element of the white light emitting diode lamp is small, the white light emitting diode lamp is frequently used by being incorporated into a backlight of a liquid crystal displaying device and a cellular phone and the like. A white light emitting diode used in this white light emitting diode lamp includes a light emitting diode element that emits a short wavelength light such as a blue light; and a fluorescent substance that is excited by absorbing a part of or all of this light and emits a fluorescent light with a longer wavelength such as a yellow light. In other words, white light is obtained by mixing a blue light emitted by a blue light emitting diode as a light source and a yellow light emitted by a phosphor.
Concerning light emitting devices used for illumination, white light emitting devices with various color temperatures are demanded according to their usage. In order to meet such demands, a phosphor that provides a much wider chromaticity range compared to known phosphors, and a technology for adjusting the chromaticity are in demand.
For example, Japanese Unexamined Patent Application, First Publication No. 2002-363554 (corresponding patent: Japanese Patent No. 3668770) (Patent Document 1) discloses a phosphor such that, if a general formula is MexSi12−(m+n)Al(m+n)OnN16−n, Me is Ca, Mg, Y; or a lanthanide metal excluding La and Ce; and Ce, Pr, Eu, Tb, Yb, and Er which are emission center lanthanide metals replacing a part of it; and a Dy as its coactivator. Regarding this phosphor, a composition range is disclosed such that, when the metal Me is divalent, 0.6<m<3.0 and 0≦n<1.5; and when the metal Me is trivalent, 0.9<m<4.5 and 0≦n<1.5. It is also disclosed that, the peak emission wavelength can be continuously varied in the range of 560 nm to 590 nm by changing the activator amount of the Eu2+ ion. A phosphor disclosed in Japanese Unexamined Patent Application, First Publication No. 2003-124527 (Patent Document 2) achieves a dominant wavelength in the range of 546 nm to 583 nm by being activated by Eu2+ and having Ca as a main component of metal. In PCT International Publication No. WO 2006/006582 (Patent Document 3), we disclosed a phosphor having a dominant wavelength in the range of 577.7˜583.1 nm by being activated by Eu2+ and by having Ca as a main component of metal. However, presently there is a demand for a phosphor that can be excited by a blue light and emits light at a much longer wavelength compared to the above disclosed phosphors.